The present invention concerns collector-type D.C. machines, either motors or generators, having a multi-pole stator magnet arrangement and an ironless rotor winding comprising a plurality of rotor coils lower in number than the number of stator poles, the rotor coils being arranged as a single-layer winding, with the collector of the machine comprising collector lamellas of which predetermined ones are electrically interconnected by cross-connecting means. Such a machine is disclosed, for example, in commonly owned Federal Republic of Germany patent application No. P 32 17 283.4.